Make Magazine - Volume 33

ZEN CART language. If Processing took Java’s graphical power
and made it easy for kids, artists, and designers,
FREE \\ zen-cart.com Arduino did the same thing with C++’s power to
Zen Cart is one of the world’s most popular open make cool stuff with embedded devices.
source online store programs. A 2003 fork from
osCommerce, it’s PHP-based, uses a MySQL PROPELLER
database, and is readily hacked and customized to
meet your particular needs, with a wide variety of FREE \\ parallax.com/tabid/832/Default.aspx
features available either natively or through free The Propeller is a microcontroller unlike any
adds-on. Google its name, and the first three hits other; it has eight cores (called cogs) running
are from big commercial shopping cart providers independently, in parallel, sharing memory and
who are trying to persuade you not to use it. What other resources. For quite a while you could only
better endorsement could you ask for? Our pals program the Propeller in Assembly or in a higher-
at Adafruit have been using it since 2005, and are level language called Spin. More recently Parallax
a great resource to help you get started. has provided tools for programming the Propeller
using the open source C toolchain.
WORDPRESS
VISUAL STUDIO
FREE \\ wordpress.org EXPRESS/NETDUINO
WordPress (WP) is the most popular blogging and
online content management platform in the world FREE \\ netduino.com/downloads
today. It’s free, open source software, written in Despite the -duino suffix, Netduino is not Arduino.
PHP, and using a MySQL backend, which allows it You can’t grab the Arduino IDE, plug in a Netduino,
to be installed on almost any web server. Overall, and expect anything interesting to happen. The
WP achieves an amazing balance between user- “Net” in Netduino refers to .NET, Microsoft’s
friendliness and advanced customizability. Themes development platform. Many years ago, Microsoft
control how content is visually presented on a page, tried an experiment called SPOT (Smart Personal
plugins offer extended functionality like search Object Technology) that was probably a bit ahead
engine optimization and rich commenting, and wid- of its time. Instead of being crushed up and spit out,
gets allow for easy custom page layout. And WP’s Microsoft decided to put the whole thing out under
extremely active user community is constantly the Apache 2.0 open source license — compilers,
working to tweak and develop them all. Great runtime, and tools — as the .NET Micro Framework.
mobile apps are available for WP, as well, so you Even though it’s open source, you still need a devel-
can take your blogging on the go. opment environment, which is where the closed-
source Visual Studio IDE comes in. While it’s pos-
MICRO- sible to develop Netduino programs with a 100%
CONTROLLERS open source toolchain (using the Mono Project), it’s
painful. Visual Studio Express gives you an easy way
Software to get the most out of your to develop and deploy Netduino programs.
Arduino or other microcontroller.
ENERGIA (MSP430)
ARDUINO
FREE \\ energia.nu
FREE \\ arduino.cc This is a port of the Arduino development environ-
This is the software package you need to get your ment (everything from the IDE to the compiler tools
Arduino to do something other than run the pre- that run under its hood) to the Texas Instruments
installed “Blink” sketch. You use the Arduino IDE MSP430 microcontroller family. It feels just like
(integrated development environment) to write pro- Arduino, and you can pretty much use the same
grams (known as sketches among Arduino users), code you use on Arduino (though you’ll need to
and load them onto your Arduino board. Within the change your pin assignments to match the board
Arduino IDE, you’ll use a prettied-up variant of C++ you’re using). This is a great development envi-
that was inspired and informed by the Processing ronment for exploring the inexpensive MSP430
LaunchPad from Texas Instruments.

makezine.com 49

FEATURES SOFTWARE FOR MAKERS

PROGRAMMING MIT APP INVENTOR
FOR KIDS
FREE \\ appinventor.mit.edu
Entertaining and useful programs to Inspired by Scratch, App Inventor is a project that
pique kids’ interest in software and was originally created at Google to bring Scratch-
make programming accessible. like programming to Android phones. Kids can drag
and drop blocks together to create working pro-
PYTHON grams, and then deploy them to Android devices.
When the App Inventor project lead, Hal Abelson,
FREE \\ python.org finished his sabbatical at Google and returned to
Python is a great first programming language MIT, he brought it back with him.
(or scripting language). It’s clear, easy to get up and
running, and the Python community has created MODKIT
lots of libraries that will do what you need. Python is
an interpreted language, which means that you can FREE \\ modk.it
write a program (or script) and execute it directly Intended to be intuitive enough for kids to use,
rather than compiling it into machine code. Modkit is a browser-based Scratch-like program-
ming platform for the Arduino. Once you write a
SCRATCH program by dragging and dropping colored blocks,
you can examine the Processing code it generates,
FREE \\ scratch.mit.edu and edit it directly in Processing.
This graphical programming language was
developed at MIT to teach kids how to program ALICE
and think creatively. By dragging, dropping, and
connecting colored blocks, you can create games FREE \\ alice.org
with animation and sound effects. Not just for kids (but perfectly suited to them),
this educational software from Carnegie Mellon
“It is our responsibility to equip children University is aimed at teaching object-oriented
with the knowledge necessary to under- programming in a 3D environment. Using the drag-
stand our world and to have a host of and-drop interface, students visually learn to ani-
options in it and I believe that programming mate 3D objects and become engaged in
can play an integral part in this.” programming through storytelling.

—Michael Kohl HAPPY NERDS

FREE \\ happynerds.net
Austrian software engineer Michael Kohl has
put together this site as a resource dedicated solely
to programming for kids. Under each category
(Windows, Mac, Linux, Browser, and Books),
Kohl provides healthy lists and links to learning
resources. He writes, “It is our responsibility to
equip children with the knowledge necessary to
understand our world and to have a host of options
in it and I believe that programming can play an
integral part in this.”

By Lynn Langit

“Thinking like a programmer”
is a great way to interact with
your computer. Programming
itself is satisfying because
you can make whatever you
can imagine.

Breaking a problem down into concrete steps that software downloads, recipes, tips, and answer keys
you can then test out one at a time is part of the there. We also have videos of each recipe being
maker mentality. Thinking like a programmer will coded line-by-line in the Teachers section of the
help you in other places too; for example, when TKP website.
you’re trying to solve math problems.

SmallBasic is an introductory programming lan-
guage, based on Microsoft .NET. The language and
its editor (also known as an integrated development
environment, or IDE for short) is a free download.
SmallBasic recipes are free, fun lessons you can
use to teach yourself how to program computer
graphics, make simple games, and do other things.
Recipes are designed for kids ages 10 and up who
have basic keyboarding skills.

In the screen shot (right), you can see an exam-
ple recipe called Pentagon Crazy.

To use recipes, you’ll also need to download the
SmallBasicFun extensions and follow the instruc-
tions for installing them inside SmallBasic. These
extensions add objects, examples, and more to
SmallBasic itself, making programming easier and
even more fun. Get them here: extendsmallbasic.
codeplex.com.

SmallBasic recipes are part of the “Learn to
Program Courseware” found at TeachingKids
Programming.org (TKP). You’ll find links to all of the

makezine.com 51

FEATURES SOFTWARE FOR MAKERS

HOW DO I GET STARTED?

All the steps are listed on the TKP website,
but we’ll also list them here:

1. Grab a PC with Windows XP, Vista, or 7 and
.NET 3.5 SP1 or greater.

2. Download and install SmallBasic and the exten- I’M STUCK
sions on your PC, or download our SmallBasicOnUSB
zip file (makezine.com/go/smallbasiczip) onto When you get stuck, we’ve got many tips for you to
a flash drive, unzip it and plug it in to your PC. try out. What to do depends on how you’re stuck.
Then click the SB.exe file to get started (no
install required).

3. Browse the SmallBasic recipe library and pick a Error Message
recipe to start with. Import the ID# into SmallBasic
and start translating the English comments into One kind of stuck is that you get some error mes-
SmallBasic code. We suggest you start with the sage at the bottom of the IDE. For example, you see
SQUARE recipe and then work your way down the that the error says “14,12: Operation ‘Tortoise.Turn’
recipes page (recipes are listed from easy to hard is supplied 0 arguments, but takes 1 arguments.”
on that page).
For this kind of stuck we suggest you double click
4. After you’ve on the error message text (read it first!) and then
click on the line of SmallBasic code that is causing
TIP Code with a friend: translated each the error. Take a look at the example (right side
(single) line highlighted) and update as needed. You can even
this process of working is of English into copy and paste the example from the documenta-
tion if need be. We call this “fake it ‘till you make it.”
called “pair programming.” To SmallBasic code, Your goal here is to get your code to run.

do pair programming, just take RUN the code You can always also just “Undo” until you get
turns on the keyboard. One (using the F5 key) back into a state that will run and then try another
kid types while the other kid to make sure that SmallBasic word.
talks (that is, tells the kid who your translation
is typing what to type). Make was correct. Unsure of What to Do

sure you swap roles regularly 5. Delete the English Another kind of stuck is that you don’t know the
SmallBasic word(s) to use to translate one or more
— we suggest every 5 minutes comment after of the English comments. Here we suggest using
or so. It’s best if you actually you’ve got your the Ctrl+Spacebar keys to get a list of all possible
stand up and switch places code right. words. If you know the Object (noun), but can’t find
the Operation (verb), try looking at other Objects
as you go along. 6. Pick your next to see if a more appropriate Operation is listed with
that object. For example, if you need to center a
line to translate. shape at a given x,y location, you would want to
use the ShapeMaker object (rather than the Shapes
Pick a line you can test by running your program. object) as ShapeMaker includes an operation
named CenterShapeAt().
For example translate “Move the Tortoise 50 pixels”
Weird Results
before “Make the Tortoise move as fast as pos-
Yet another kind of stuck is code that will run
sible.” You can also watch a short video on coding (meaning there are no errors shown when you try to

up a mini-recipe (called the Giant Tortoise) to see

coding with SmallBasic in action: makezine.com/

go/tortoise.

52

Here’s an example of what you can turn a square into with just a few changes to your code.

run it), but runs in a weird way, such as an all-white ON MY OWN
program window where you had expected to see
the Tortoise or Turtle objects drawing something. After you finish translating a particular recipe, you
This can be caused by a number of errors, the most can tinker with the code to make it into something
common of which are incorrect End statements for slightly (or even very) different than what you
Loops, Conditionals, or Subroutines. Check the posi- started with, e.g., change a square into a spiral.
tion of your EndFor, EndIf, and EndSub statements. Look at the “Variation Images and Information”
(Again, you may want to use the Undo feature to section for each recipe for suggestions, cheat
get back to a runnable state.) sheets, and more.

You can also use the Cheat Sheet provided for BEYOND SMALLBASIC
each recipe, which shows you the SmallBasic code.
It also indicates which lines of English should be If you click the “Graduate” button in the IDE it
translated into code first, so you can actually see will translate your code to VisualBasic.NET. To
the results as you go along. edit VB.NET you’ll need the Visual Studio IDE.
Download either VB Express (free), or sign up for
DreamSpark to get a full version of Visual Studio to
work with.

At the TKP site there are also recipes for other
programming languages (such as Java, T-SQL
for databases, and more). There are lessons for
Microsoft Kodu as well — a programming language
designed for children as young as 6 to get started
creating worlds and games via visual programming.

Enjoy working with SmallBasic Recipes!

We know that you'll be making cool stuff with SmallBasic, and we want to see and share what
you’ve done. You can publish your variations by clicking the Publish button in SmallBasic. Then
you’ll get an ID number. You can share that ID with your friends and they can see your varia-
tion and work together with you on making your program even cooler.

Lynn Langit is a professional programmer and technical educator, and is also co-founder of TKP, a U.S. nonprofit. She authors and teaches courseware for
data solutions. Lynn blogs at LynnLangit.com and TeachingKidsProgramming.org.

makezine.com 53

FEATURES SOFTWARE FOR MAKERS

By Eric Rosenbaum and Amos Blanton

Kids get wide-eyed when they realize they can click and move the mouse cursor, too). You can play
make music just by tapping on a row of bananas. games on a controller drawn in pencil, make music
Adults start jamming out on classic tunes, and then with fruit, advance your PowerPoint slides by taking
inevitably somebody discovers that they can play bites from a pastry, take a picture of your cat when
a sound by connecting two people: a high-five, it takes a drink, or navigate Google Earth with your
or even a kiss, can trigger a cymbal crash. bare feet (check out the video at makeymakey.com
to see lots of fun examples).
It’s all possible thanks to MaKey MaKey, a
new invention kit developed by Jay Silver and One of the most powerful ways to use MaKey
Eric Rosenbaum. First you alligator clip everyday MaKey is to combine it with Scratch, a free and
materials like bananas, Play-Doh, or your grandma easy-to-use graphical programming language we
to the MaKey MaKey circuit board. Then you helped create as part of the Lifelong Kindergarten
plug it into your computer, which thinks MaKey group at MIT Media Lab (see scratch.mit.edu).
MaKey is a USB keyboard. Now, when you complete Scratch lets you make stories, games, and ani-
a circuit through the bananas (or anything even mations just by snapping blocks together on the
a tiny bit electrically conductive), the computer screen. It’s easy to make things happen when a
thinks a key has been pressed. key is pressed. There are few limits to what you
can create with Scratch and MaKey MaKey. Here
MaKey MaKey works with just about any soft- are a few projects we made to get you started.
ware you’ve already got, because it works like a
keyboard that lets you make your own keys (it can

54

BANANA PIANO

How do you make a banana into a piano key? First We made a piano in Scratch, with different notes
we’ll set up MaKey MaKey so you can complete a triggered by the up, down, left, and right arrow
circuit by touching a banana. keys, by the space bar, and by a mouse click. Each

Connect yourself to ground, banana is plugged into one
and a banana to “space” on the of those inputs on the
MaKey MaKey. Now, when MaKey MaKey. To connect
you touch the banana, the the person to ground so they
computer thinks the space can complete the circuit,
key was pressed. we like to use a lime.
What other musical instruments could you
Next we’ll set up Scratch to play a sound when make? Lots of different types of fruit, vegetables,
you press the space key (or touch a banana). and other food will work for making pianos. You
can play with other sounds, too. Can you make a
Just put these blocks (above) together in Scratch, drum kit out of cheese? How about a squishy sound
and when you press the space key, it will play a effects machine made out of a few marshmallows?
piano note.

Now that you’ve got one banana working, we can
set up some more keys and play some tunes!

makezine.com 55

FEATURES SOFTWARE FOR MAKERS

Each time the horse rocks
to the back or the front,
Scratch steps the animation
forward by one frame.

ROCK-AND-ROLL
ROCKING HORSE

Tired of the usual game controllers? We decided to We imported the GIF into Scratch, creating a sep-
make a wooden rocking horse into a whole new kind arate costume for each frame. (In Scratch, objects
of controller using MaKey MaKey and Scratch. First that perform functions are called sprites, and each
we made two simple switches
that close when pressure is frame of a sprite is a
applied — we made ours out costume.) Then we used
of clothespins and foil. We Scratch blocks to advance
attached one to the front and to the next costume at
one to the back of the rocking each rock, creating the illu-
horse’s rail. When the horse sion of movement — just
rocks, the clothespins press as Muybridge discovered.
together, completing a circuit The faster you rock, the
so that MaKey MaKey presses faster the horse runs.
a key. What else could you control with your own rock-
ing horse? Maybe it needs a carrot you can feed
For our Scratch animation, we used an animated to it, or some head-mounted lasers.
GIF of a horse running made from photographs cre- What other toys can you turn into controllers for
ated by Eadweard Muybridge back in the 1870s. your own games in Scratch?

56

Door Knocker
of Doom

We wanted to create an interactive Halloween scare at
the front door, using a MaKey MaKey and a computer
running Scratch showing in the window. We experiment-
ed with the brass door knocker and found that it was
conductive. Then we connected two clips to it: one on the
base, connected to ground on the MaKey MaKey, and the
other on the handle of the knocker, connected to “space.“
The knocker normally sits touching the base, so Scratch
will think you’re holding down the space key until you lift
the knocker. Our little Scratch program waits until you lift
the knocker, and then plays sound and animation.

Our example just makes the Scratch cat say “boo.”
What terrifying animations and sounds will you create?
You can draw scary scenes using Scratch’s built-in paint
editor, or import other photos and graphics, then make
them come to life using the motion and graphic effects
blocks. You can record your own horrifying sounds, or
find sounds online. You can also try connecting your com-
puter to a projector or speaker system for bigger, louder
effects. And of course, it’s not just about door knockers:
you can use anything that makes or breaks a circuit.

Other Ways to Connect Scratch to the Physical World

MaKey MaKey isn’t the only way to create cool physical-digital projects with Scratch.
Here are two other Scratch-compatible tools.

PICOBOARD LEGO WEDO

The PicoBoard (aka Scratch Board) is an open The WeDo is a robotics kit developed by Lego for
source sensor board available from SparkFun. kids ages 7 and up. You can control your Scratch
It can sense levels of light and sound, the position projects with the WeDo’s distance and tilt sensors,
of its built-in slider knob, the state of its button, and and activate the WeDo’s motor to create moving
the resistance between each of its four electrical mechanisms. The WeDo is available online through
inputs (which come with wires and alligator clips). the Lego education website.
Scratchers have used PicoBoards to make every-
thing from controllers for interactive games to
sophisticated alarm systems.

Eric Rosenbaum is a Ph.D. student in the Lifelong Kindergarten Group at MIT Media Lab. He’s a member of the Scratch team and co-creator of MaKey
MaKey. Amos Blanton is the online community coordinator for Scratch. He designs and sustains supportive learning environments for people with agency.

makezine.com 57

SKILLBUILDER Gregory Hayes

INTERMEDIATE

58

CNC Panel
Joinery

A guide to making interlocking, self-aligning,
and demountable joints in flat stock. BySeanMichaelRagan

Gregory Hayes I’VE BEEN COLLECTING CLEVER WAYS ing to. Generally, I’ve tried to use descriptive
OF SLOTTING flat stock together since I first terms instead of “proper” names to avoid con-
read Victor Papanek and James Hennessey’s fusion, but here and there I may have slipped
Nomadic Furniture back in 1999, well before up and called a rose by some other name.
the advent of the accessible hobby-class
CNC tools that make manufacturing parts To simplify things, I’m only considering
like these pretty easy today. Now the world joints between two panels, using all-the-way-
is full of people designing models, project through cuts, orthogonal to the plane of the
enclosures, sculpture, furniture, and all kinds stock. For a taste of how complex this subject
of other cool stuff to be assembled from parts can become without these limitations, check
made on laser cutters and CNC routers. out Jochen Gros’ “50 Digital Wood Joints”
project at flexiblestream.org/project/
I keep expecting a definitive book or website 50-digital-wood-joints.
to emerge that covers the “bag of tricks” in
an organized way. So far, I haven’t found it. Laser vs. Rotary Cutters:
Perhaps this article can serve as a jumping- The Inside Corner Problem
off point.
Hobby-class laser cutters and CNC routers
In presenting this material, I want to first each have advantages and disadvantages.
acknowledge my respect for the world’s Laser cutters can cut much finer details
established and ancient traditions of joinery. because they have very small kerf, or width
I do not for a moment imagine that any of this of cut. On the other hand, they’re more expen-
is fundamentally new. But I do see a need to sive and can’t do partial-depth cutting or
organize this information to address the needs “pocketing” like a CNC router can. They also
of the small CNC tool operator who wants use heat, which can burn the substrate and/
to make interlocking, self-aligning, and/or or generate nasty off-gassing. However, the
demountable joints in flat stock, for instance burning effect can be used decoratively.
plywood or sheet plastic.
A CNC router can change bits and cut
I may abuse some terms without mean- complex relieved surfaces, or make cuts with

makezine.com 59

SKILL BUILDER B
D
A
C

EF

mitered or otherwise profiled edges. I don’t this may be OK, but doing so leaves a void in Sean Michael Ragan
think either tool can be described as simply the center of the joint and concentrates stress
“better,” and with one minor caveat, all of the on the radiused corners.
techniques presented here can be used equal-
ly well with either a laser cutter or a router. A better solution is shown in Figure C.
Now the inside faces of the edge laps mate
Because of its very small cutting channel, cleanly. On the other hand, the round divots
a laser cutter can produce an inside corner are visible in the assembled joint. If that both-
with a sharp angle, whereas a rotary cutter ers you, of course, you can also do it as shown
using a physical tool is limited to inside cor- in Figure D, if your cutter is narrow enough.
ners rounded at the cutting tool’s radius. The On average, this method offers the best com-
laser-cut version, with its sharp 90° corners, promise; the flat areas between the divots
is suitable for use in a simple edge-lap joint seat against each other firmly and the divots
(Figure A). themselves are concealed inside the joint.

The router-cut version, however, just To simplify presentation, the joints in the
doesn’t work. The radiused corners bump rest of this article are presented with ideal
into each other and the part edges don’t line “laser cut” inside corners. But all of them
up (Figure B). You can cut each slot a bit should be readily adapted to rotary cutting
deeper, of course, and in some applications by using the divot method.

60

GH
IJ

K

Biasing Cross (“X”) Joints

Many of these joints are symmetrical, and Figure G shows a version of the basic slotted
can be assembled in more than one way. The edge lap joint, in which one side has an integral
joint in Figure E, for instance, can be assem- snap-lock feature. The snap hooks are acces-
bled in two different ways (four, if approaches sible from the end of the joint. Insert a small,
from below are allowed). Which is correct? flat-blade screwdriver, pry a bit, and they can
be popped loose and the joint opened again.
Often it’s possible to deliberately break
this symmetry so that the parts can only be But move the hook and the catch away
assembled in one way, or in fewer or more from the edges of the stock, and the snap-
obviously correct ways. For instance, the lock action becomes irreversible (Figure H).
joint in Figure F can still be assembled, but Note that both pieces of stock could include
the disfavored orientations are more clearly both hooks and catches. I’m only showing
wrong because the part edges no longer align. “one-sided” snapping joints for clarity.

This trick can be very handy in complex Replace the hook with a bulge, and the
structures, particularly for kit parts, to keep snap becomes a detent, meaning the part
end users from putting the joint together will stick in place but can be removed with
backwards. I call a joint that has its symmetry sufficient force (Figure I). The detent could
deliberately broken in this way biased. catch in one position, or many (Figure J).

makezine.com 61

SKILL BUILDER

L

M

N

Figure K (previous page) shows an unusual gravity can help keep the pieces engaged,
X joint that uses a radial interlocking motion. and may be biased or otherwise modified like
the T joints described below.
A biased version is also possible. Figure L
shows an X joint with the symmetry broken: Tee (“T”) Joints
shown disassembled (left), assembled in
its “favored” orientation (middle), and in its Figure P shows examples of simple mortise
“disfavored” orientation (right). and tenon type joints, or T joints. We can split
the mortise and tenon into two slots and tabs
Locks or detents can be added to the (or as many slots and tabs as we like). If we
stationary member (Figure M) and/or to the break the symmetry of the slots and tabs, the
rotated member (Figure N). Note, in this case, joint becomes biased. And if we extend the
that it doesn’t matter if the profile of the catch tab a small distance past the thickness of the
is hooked or rounded; once the catch pops stock, we can easily add snaps or detents that
into the slot, it’ll be very hard to get out. catch on the far side of the slotted part.

Finally, in the case of X joints, if one member Fasteners in the plane of one of the pieces
is narrower than the other, a full-width slotted can also be introduced. The captive square
arrangement becomes possible (Figure O). nut joint (Figure Q) is seen on a number of
commercial products featuring CNC-cut parts,
Such joints may be useful especially for
shelves or other upright applications where

62

OP

Q RS

such as the Phlatformer vacuum former kit Corner (“L”) Joints
and several popular 3D printer kits.
The arrangement of interlocking tabs
This particular configuration was the and slots at a 90° angle is ancient and
subject of a nomenclature debate on the rudimentary (Figure R). Most people call it
MAKE site, though no consensus was a box joint. It, too, can be biased by breaking
achieved. Interesting possibilities include symmetry, and it’s just as amenable to the
”captive nut joint,” “bedframe joint,” and bolted captive-nut arrangement (Figure S).
“Pettis joint” (my personal favorite, because
it observes Stigler’s Law*). There are almost * Stigler’s Law of eponymy states that no scientific discovery is
certainly other clever ways to incorporate named after its original discoverer. Allegedly discovered by Robert K.
metal fasteners or other bits of common Merton, making Stigler’s Law exemplify itself.
hardware in this type of joinery that I haven’t
seen, or that have not yet been invented. makezine.com 63

SKILL BUILDER

V

T
W

UX

Y

Oblique (“V”) Joints Coplanar (“I”) Joints

Though the captive-nut joint doesn’t really The classic finger joint is used to join mem-
work unless its two parts are at right angles to bers in the same plane for gluing (Figure V).
one another, generally L joints can be pressed The interlocking bulbed version in Figure W
into service for acute or obtuse angles, as doesn’t depend on glue for its strength in ten-
well (Figure T), making V joints. sion. If left unglued, of course, these flat joints
require some means to keep the two pieces
The bottoms of the slots no longer index in the same plane when the joint is in use.
closely against the surface of the stock, but if
the members are held in alignment by some Figure X shows a variation of the bulb
other means, for example by glue or the intro- joint that allows for in-plane hinging action.
duction of a third panel, it may not matter. I want to call this a “Kanelba hinge,” for George
S. Kanelba of New York, whose Cube Desk
An interesting variation on this method, project in the 1984 Popular Science book
in which the fingers are rounded (Figure U), 67 Prizewinning Plywood Projects is the only
has been used by Belgian designer Sebastien place I’ve ever seen it. Kanelba hinges can be
Wierinck. Though rounded fingers may look daisy-chained to make “snakes” (Figure Y).
better, it should be mentioned, they will limit The individual hinges, of course, can be set to
the surface area available to any adhesive stop at angles other than 90°.
that might be used to glue the joint.

64

Z

AA BB

Flexures will have to be longer to achieve the same
degree of flexibility, because the router slots
Though not strictly joints, there is a class will have to be considerably wider.
of clever CNC tricks that meet the rules of
our game, and that are designed to exploit the Finally, Figure BB shows an oddball spiral
natural elasticity of the panel material itself technique, courtesy of PlasmaCAM. Originally
to create living hinges, springs, and other cut out from sheet steel using a CNC plasma
dynamic flexing elements. We have already cutter, a similar idea could work with a laser
broached the subject of integral flexures with cutter or a mill, in some other material.
our discussion of catches and detents.
Final Thoughts
Figure Z is an in-plane spring or living
hinge element that is kind of like kerf-bending, This is a huge area, and this article only just
but with “thru” cuts. If not constrained to scratches the surface. While compiling it, new
motion in the plane, such a feature will be variations and ideas kept occurring to me, as
pretty unstable. I suspect they will to you, reading it. The rules
of the game, again, are simple: all-the-way-
Figure AA shows a version more suitable through cuts, 90° to the surface of the stock,
for out-of-plane bending. This is the some- only one or two cut parts involved. What
what famous Snijlab living hinge technique clever tricks have I missed? Let me know,
(which I believe should be called a sninge), an in the comments of the original post at
accordion-cut pattern that allows for stable makezine.com/go/cncpanel. a
out-of-plane flexing (see Laser-Cut Book
Covers, page 66). It’s most commonly execut- Sean Michael Ragan is technical editor of MAKE magazine. His work has
ed in laser-cut plywood, but there’s no reason appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall
it couldn’t be cut with a CNC mill and/or in Street Journal.
other materials. A router-cut sninge, however,

makezine.com 65

PROJECTS LASER CUT BOOK COVERS

Use this neat
technique to make
plywood flexible.

By Christian Waber and
Jiskar Schmitz

a TIME: 1 HOUR a COMPLEXITY: EASY

Laser-Cut Book Covers

By making a pattern of laser cuts in a turn. That’s how the hinge we use here works. Jiskar Schmitz
flat piece of wood, you can easily create When you look closely you can see that the
hinges, clamps, and other features. cuts leave a pattern of interconnected small
“sticks.” When you bend the cover, you’ll see
We made wooden booklets, each with a hinge them all twisting a little bit.
and a notepad holder. The hinge can be fully
bent in both directions repeatedly without There are several patterns that will allow
breaking. How is that possible? First, wood bending. The simplest one is a set of shifted
has the strength to withstand repetitive bend- cuts, as shown in Figure A. The longer or
ing and twisting. It won’t break as long as the wider you make the piece, the softer it gets.
stresses stay under a certain limit. This pattern yields a very springy hinge that
you can move in all directions.
The trick to making the wood flexible is to
break it up in a lot of small pieces that can all To make the hinge stronger, you can add
twist a little. All these tiny twists add up so some tabs in each line (Figure B). This gives
you can bend the sheet without stressing the the hinge a lot more strength while still allow-
material too much. ing you to bend it.

Imagine it like this: when you twist a match- Inside the cover is a clamp that holds
stick with your hands, you can twist it maybe the notepad with two flexible “arms,” cut
1 of a turn before it breaks. Imagine now so they're slightly smaller than the notepad
you have a matchstick 10 times longer. You (Figure C). When you insert the notepad,
can twist it 10 times as far, more than a full the arms press on the sides, keeping it
firmly in place.

66

MATERIALS & TOOLS A

» Plywood, approx. 4mm Birch works best.
» Notepad, A7 size
» Rubber band
» Clear varnish
» Wood glue
» Sandpaper, 180 grit
» Laser cutter If you don’t own one, check

your local fab lab, hackerspace, TechShop,
or a commercial laser-cutting service.

1. Download the DXF files from

Thingiverse (thingiverse.com/thing:
12707). Load up your plywood, then
send the files to the laser cutter.

2. When the pieces are ready,

sand them to get rid of the laser-
cutting marks.

3. Varnish both pieces to protect

them from dirt. Set aside to dry.

4. When dry, apply wood glue to B

the back of the clamp's middle
section and position it on the inside
of the cover. Take care not to put glue
under the ribbed “arms” of the clamp
because these need to move freely.
Put some weight on the clamp and
wait 2 hours for the glue to dry.

5. Carefully insert the notepad in the

clamp, insert the rubber band in the 2
slots at the bottom, and you’re done! a

C

Mod It!

Once you’ve downloaded the DXF
files, there’s nothing stopping you
from altering them to fit your own
needs. Go ahead and change the
shape to your liking, or laser cut your
name onto it. You can also extract
the hinge and use it in other projects
that need some bent wood. Happy
making and don’t forget to share
your work!

Gregory Hayes Christian Waber and Jiskar Schmitz are from the Netherlands.
They founded the digital manufacturing company Snijlab
(snijlab.nl) to make the full power of digital fabrication acces-
sible for everyone. They love to design, make, and engineer.

makezine.com 67

PROJECTS RASPBERRY PI

This project is from Getting
Started with Raspberry
Pi by Matt Richardson and
Shawn Wallace. It assumes
that you already know how
to set up and operate the
Raspberry Pi platform, and
that you know the basics
of the Python programming
language. If you want to
get up to speed quickly,
you can find all of the
above (and much more) in
Richardson and Wallace’s
book, available in the Maker
Shed (makershed.com).

68

An introductory
exercise for
Raspberry Pi.

By Matt Richardson

SiomunpldeboardandShawnWallace
a TIME: 1 HOUR a COMPLEXITY: INTERMEDIATE
In this simple breadboard build, we’ll 1. Breadboard the circuit.
use a Raspberry Pi and the sound
functions of the Pygame module in Using a female-to-male jumper wire, connect
the Python programming language the Raspberry Pi’s ground pin to the negative
to make a soundboard. A soundboard rail on your breadboard.
lets you trigger the playback of
sounds when you push its buttons. With another female-to-male jumper wire,
connect the Raspberry Pi’s 3.3V pin to the
You’ll also need a few uncompressed sound positive rail on your breadboard. Insert the 3
files, in WAV format. You can record or down- pushbutton switches into the breadboard, all
load your own, and there are a few sound straddling the center trench.
files preloaded onto the Raspberry Pi in /usr/
share/sounds/alsa/ that you can use for test- Now with standard jumper wires or small
ing. We even collected a few public domain pieces of hookup wire, connect the positive
sound effects from The Internet Archive that rail of the breadboard to the top pin of each
you can download at makeprojects.com/v/33. button. Next, add the pulldown resistors.
These will give you some fun files to play with Connect the bottom pin of each button to
right away. ground with a 10K resistor.

Connect each button’s bottom pin (the one
with the 10K resistor) to the Raspberry Pi’s
GPIO pins using female-to-male jumper wires.
For this project, we use pins 23, 24, and 25.

About Python

Gunther Kirsch » Python (python.org) is a great to teach programming in the explicitly tell the computer
first programming language; elementary and secondary whether a variable is a number,
it’s clear and easy to get up and grade schools using Python. a list, or a string; the interpreter
running. More importantly, More than a decade later, this figures out the data types
there are a lot of other users is actually happening with the when you execute the script.
that you can share code with coming of the Raspberry Pi.
and hit up for questions. » The Python interpreter
» Python is an interpreted can be run in 2 ways: as an
» Guido Van Rossum created language, which means that interactive shell to execute
Python, and very early on rec- you can write a program or individual commands, or as
ognized its use as an accessible script and execute it directly a command-line program to
first language for computing. In rather than compiling it into execute stand-alone scripts.
1999 Van Rossum put together machine code. Interpreted The integrated development
a widely read proposal called languages are a bit quicker environment (IDE) bundled
“Computer Programming for to program and have a few with Python and the Rasp-
Everybody” that laid out a side benefits. For example, berry Pi is called IDLE.
vision for an ambitious program in Python you don’t have to

makezine.com 69

PROJECTS RASPBERRY PI

NOTE WhilePygame

is available for Python 3,
on the Raspberry Pi’s
default installation, it’s only
installed for Python 2.7.

MATERIALS

» Raspberry Pi with power,
keyboard, monitor, and network
connected

,» Pushbutton switches (3)

» Jumper wires female-to-
male (5)

» Standard jumper wires (3)
or hookup wire cut to size

» Solderless breadboard
» Resistors, 10kΩ (3)
» Computer speakers or an HDMI

monitor that has built-in speakers

70

2. Work on the code.

Create a new directory in your home directory called soundboard. Open that
folder and create a file there called soundboard.py. Open soundboard.py and
type in the following code (or download it from makeprojects.com/v/33):

import pygame.mixer Initialize Pygame’s mixer.
from time import sleep
import RPi.GPIO as GPIO Load the sounds.
from sys import exit
Set up 3 channels, one for
GPIO.setmode(GPIO.BCM) each sound, so that we
GPIO.setup(23, GPIO.IN) can play different sounds
GPIO.setup(24, GPIO.IN) concurrently.
GPIO.setup(25, GPIO.IN)
Let the user know the
pygame.mixer.init(48000, -16, 1, 1024) soundboard is ready.

sndA = pygame.mixer.Sound("buzzer.wav") If the pin is high, execute
sndB = pygame.mixer.Sound("clap.wav") the following line.
sndC = pygame.mixer.Sound("laugh.wav")
Play the sound.
soundChannelA = pygame.mixer.Channel(1)
soundChannelB = pygame.mixer.Channel(2) Don’t “peg” the processor by
soundChannelC = pygame.mixer.Channel(3) checking the buttons faster
than we need to.
print "Soundboard Ready."
This will let us exit the script
while True: cleanly when the user hits
try: CTRL+C, without showing the
if (GPIO.input(23) == True): traceback message.
soundChannelA.play(sndA)
if (GPIO.input(24) == True):
soundChannelB.play(sndB)
if (GPIO.input(25) == True):
soundChannelC.play(sndC)
sleep(.01)
except KeyboardInterrupt:
exit()

Gregory Hayes Go to the command line and navigate to To send the audio through HDMI to the
the folder where you’ve saved soundboard.py monitor, use:
and execute the script with Python: $ sudo amixer cset numid=3 2
$ sudo python soundboard.py
Of course, you aren’t limited to just 3
After you see “Soundboard Ready,” start sounds; you can add quite a few more. Just
pushing buttons to play the sound samples. add the files to the soundboard directory and
Depending on how your Raspberry Pi is set update the code accordingly. a
up, your sound might be sent via HDMI to your
display, or it may be sent to the 3.5mm analog Matt Richardson is a contributing editor of MAKE and a Brooklyn-based
audio output jack on the board. technophile, maker of things, photographer, and video producer. His work
can be found at mattrichardson.com.
To change that, exit the script by typing
CTRL+C and executing the following com- Shawn Wallace edits books for MAKE and lives in Providence, R.I. His work
mand to use the analog audio output: can be found at fluxly.com.
$ sudo amixer cset numid=3 1

makezine.com 71

PROJECTS DIY WELDING ROD

DIY
Welding
Rod
a TIME: 1 HOUR a COMPLEXITY: EASY

Prepare for the There are a bunch of DIY welder articles and Becky Stern
zombie apocalypse how-tos out in the ether, ranging from the super
by rolling your own. simple, dumb, and brutally effective (3 car bat-
teries wired in series) to the high-tech and fancy
Written by Chris Hackett (TIG machines from microwave bits, oxyhydrogen
torches from split water and plumbing supplies).
72
It’s safe to say that experienced makers will be fusing
metal even if an exceptionally biblical catastrophe were to
strike the welding industry. If civilization and supply chains
collapse, the anti-zombie fences will still get built, and the
Thunderdome will be sturdy and made from steel.

However, all the DIY welders I’ve seen assume that you
have access to welding rod. For the less weld-informed,
a good, solid weld involves more than melting and fusing
metals — the weld zone needs to be free of oxygen, other-
wise the normal oxidation of metals that leads to rust,
patinas, and discoloration happens at a dizzyingly rapid
rate, accelerated by the high heat. This is not just an aes-
thetic issue — the oxidation happens inside the weld, so
instead of a solid metal bond, you get a brittle foam filling.

Rod Research contact with the rod. The elec- MATERIALS
trodes are then dried out.
» My first step was to look » Silica gel packets (2–3) usually
up patents, which lay out the » The rod is the electrode and labeled “Desiccant: Do Not Eat”
crucial core of a technology. filler; the paper/sodium silicate and packaged with electronics,
Often, the making process is wrapper spews out shield- shoes, and other things that
laid out as well, protecting the ing gas upon combustion and hate dampness
inventor’s rights to the means, provides a path of plasma to
as well as the ends. This keeps guide the arc. The rod does not » Lye, 100% sold as drain cleaner
patent attorneys employed, deposit a protective ceramic » Steel wire or coat hanger, 2'
and provides a nice step-by- slag like modern welding rods,
step for writers to rip off. but, as Mr. Smith stated in the or more to cut into welding rods
patent, “I have found, also, that » Newspaper
» I dug up the patent “Electrode the coating of slag produced by » Plastic cups (3)
for Arc Welding,” filed in 1918 the use of known covered elec- » Nitrile or latex gloves
by Reuben Stanley Smith, a trodes is not essential to the » Stir sticks, plastic or wooden
prolific inventor and resident production of eminently satis-
of Milwaukee, Wis. Basically, factory work.” I tweaked the TOOLS
a steel rod is wrapped in cellu- patent procedure a little to use
lose (paper) soaked in sodium commonly available materials. » Digital pocket scale
silicate, and the wrapping » Hot plate to cook the lye and
is crimped to maintain close
silica gel into sodium silicate
» Pliers
» Safety glasses or goggles
» Cooking vessel, tempered

glass or nonreactive ceramic
don't use metal or Bad Things
might happen
» Toaster oven to cook the rods.
A rod oven, or some time in the
sun, should do the trick as well.
» Mortar and pestle, or scrap
of metal round stock

CAUTION Weargloves

and goggles, and weigh out the parts
individually. A little lye in the eye or
in a cut on your hand will ruin your day.

AB

Removing the oxygen is usually achieved by 1. Make the sodium silicate.
flooding the weld area with inert gas — regu-
lated, pressurized gas from a separate tank in If you have some lying around, you can skip
the case of MIG and TIG welding, or gas cre- this step. Empty out the silica gel packs until
ated from vaporizing flux in oxy-fuel, stick, and you have a pile of beads about the size of
flux-core welding. The standard, flux-coated a large walnut.
arc-welding rod is the common currency of
welding, used to hold the world together. You Get smashy with the silica gel beads. A
can get them everywhere. Until you can’t. mortar and pestle work best here. I didn’t have
one, so I rolled the silica gel package with a
Even the finest DIY welder is useless without metal rod (Figure A).
welding rod. I did a bunch of research, and as
far as I can tell no one has made their own Time for some chemistry. Zero your scale.
welding rod and documented it online. A minor Sodium silicate is made from water, silica gel,
but potentially crucial gap in the DIY world, and sodium hydroxide (lye). The proportions
solved here (and on the web at makeprojects. (by weight) are 6 parts silica gel (crushed as
com/project/d/1712). best you can), 4–8 parts lye (4 will work, 8
is stoichiometric, and anywhere in between
is fine), and 10 parts water (Figure B).

makezine.com 73

PROJECTS DIY WELDING ROD

CDE

F GH

I JK

Heat the water, then slowly add the lye 2. Prepare the rods.
while stirring (Figure C). If you just dump the
lye in, you’ll get a solid, hard lump of a caustic Straighten the coat hanger, then cut pieces
base at the bottom of your heating vessel. The of welding-rod size: about 1' long will work.
only way I found to remove it was neutralizing
it with some decently strong hydrochloric Hangers are usually covered with paint
acid. It totally looked like Science, but was or clear varnish, likely to avoid leaving your
an annoying waste of time. clothing stained with rust (I’ve never used a
hanger for the intended purpose). Sand away
Heat and stir until you get a clear but the varnish or paint until you’re left with a
ominously thick solution. Be wary, but not shiny rod of steel (Figures E and F).
too afraid — it can smell your fear.
Cut paper strips a little shorter than your
This next part can be tricky — add the silica rod. Each strip should be wide enough for
gel powder to the lye/water solution, but just 8–10 wraps around the steel (Figure G).
a little bit at a time. Take the solution off the
heat when you add the powder, then return it Paint a layer of sodium silicate onto the
to the heat while you stir. If you leave it on the paper (Figure H). You want the paper to be
heat for too long it will boil over in an instant. as saturated as possible. I found that painting
If it gets too cool the silica gel won’t go into both sides allowed the sodium silicate to soak
solution, and will clump at the bottom. in nicely and evenly.

Done right, the result will be a gummy gel, Roll the saturated paper around the steel
sodium silicate (Figure D)! rod; again, 8–10 layers will do. Try to get it as
consistently tight as possible. It’s harder than
you’d think. Smooth the layers as you go, and
smoosh the trailing edge into the rest of the

74

L MN

OPQ

RST

wrap (Figures I, J, and K). the rod burned almost as well as an off-the-
Use pliers to crimp the gooey paper tightly shelf rod (Figure O). Tons of smoke, though,
and the arc was not super stable.
and uniformly onto the rod to prevent the
coating from disintegrating faster on one side Then I welded with the homemade elec-
than another. trode (Figure P). It was splattery and ugly
(you can partially blame user error and a bit
3. Bake the rods. of a learning curve), but it definitely looks like
a weld (Figure Q). Notice the lack of ceramic
Cook the rods in a toaster oven at a low heat slag — just some ash.
for about 15 minutes. This drives out moisture,
and also makes a carbonized shell that keeps I then brushed it to see the glory of my weld.
the rods intact when stored. You want them to Looks OK, in parts. The weld side is not pretty,
be totally dry and golden (Figures L and M). but the backside shows good penetration
(Figures R and S).
4. Weld.
I chopped the weld up for a closer look,
You’re ready to test. I guess for maximum and success! No pitting, no craters, and total
punk-rock DIY points I should have tested fusion of the metal (Figure T). Welding, from
them using a car-battery welder, but the arc home-rigged rods. Take that, zombies.
welder was right there.
Hackett is a teacher (adjunct professor at New York University), artist,
I used the recommended settings for a founder and director of the Madagascar Institute (madagascarinstitute.
r" rod: DCEP, around 100 amps (Figure N). com), and television presenter (most recently on Stuck with Hackett).
Striking an arc took a couple of tries, but once
I figured out the correct distance and angle,

makezine.com 75

PROJECTS PANJOLELE

PTahne jolele
Cake Pan

Start your own
ukulele craze with

Ukulelethis great-sounding

musical instrument
built from simple
household parts.

Written and photographed by
Chester Winowiecki

a TIME: 2–3 DAYS a COMPLEXITY: MODERATE

I love making my own musical instruments.
Nothing beats the feeling of playing your own
tunes on an instrument you made yourself.
While the best instruments are made by skilled
craftspeople with high-quality materials, it
can be very rewarding to craft an instrument
with simple components at hand.

A few years ago I got interested in the idea of making
my own cigar box ukulele. I had a nice box and the wood to
make the neck but I needed a lot of other parts, like frets
and a slotted fretboard and tuners and strings, that I had
to order and wait for them to arrive. But I wanted it done
right then! So while I waited, I thought about how those
parts functioned and what I could substitute.

I remembered someone using toothpicks for frets on
cigar box guitars, and while I was wary of steel strings
cutting into the wooden frets, I thought a ukulele’s nylon
strings should be fine. Toothpicks for frets: check.

I’d also seen a lot of instruments built with cookie tins
for the body, so I headed to the local resale shop to look for
one. No tins, but what I did find was even better. Nice,
rigid aluminum cake pans, in two sizes. “Resophonic
instruments use aluminum cones, don’t they?”
I thought. Cake pans for the body: check.

I brought my treasures home and found a nice
piece of hardwood for the neck. Luckily, I had a set
of tuners and strings on hand. I got to work and
a few days later, I had a cake pan uke!

The name? Early in ukulele history, Alvin D.
Keech introduced a banjo ukulele that eventually
got the name banjolele. Looking like it does, it
seemed natural to call my instrument a Cake
Pan-jolele, or Panjolele for short.

makezine.com 77

PROJECTS PANJOLELE

Piece
of Cake

The Panjolele is like many other
stringed musical instruments

and has the same types of parts.
In essence, they’re all variable-
frequency acoustic amplifiers!

COMPONENTS Evan Hughes

A The neck is supported by F The resonator reflects some
your fretting hand and is the of the sound waves from the
platform for other parts: the back of the soundboard and
frets, the nut, and the tuners. gives the overall sound more
bass by creating a partial
B The brace goes through the enclosure.
body and is attached to the
neck. It supports the tension of G The nut stops the string
the strings so the soundboard vibration at one end, holds the
doesn’t have to. strings above the frets, and
has notches to keep the strings
C The strings are the primary spaced apart.
sound makers. When plucked,
they vibrate at a certain fre- H The frets are stopping points
quency based on their thickness, for the strings. By pressing the
tension, density, and length. string down to the fret, you
make its vibrating length shorter
D The bridge takes the vibra- and thus its pitch higher.
tions of the strings and trans-
fers them to the soundboard. I The tuners tension the
strings and allow them to be
E The soundboard acts as tuned to specific pitches.
an amplifier that makes the
vibrations louder with its
bigger surface area.

78

MATERIALS TOOLS

From a hardware store: From a music store: » Pencil
» Hardwood lumber, 1×2 » Ukulele friction tuners (set of » Ruler with e" marks
» Marking pen, fine tip
nominal, 36" length Actual 4) I’m using a basic $13 set, item » Square, adjustable
size is ¾"×1½". Choose oak, #UP26 from Elderly Instruments » Handsaw or power miter saw
maple, poplar, or other hard- (elderly.com), but for just $15 » Sanding block and sandpaper
wood, as straight and as you can get better quality tuners,
knot-free as possible. Elderly #GUKNW. in various grits
» Wood screws, #6×1¼", » Ukulele strings, concert scale » Drill or drill press
Phillips head (3) length (set of 4) I’m using a » Drill bits: 5", 1", 6", 2",
» Wood glue basic $3 set of Hilo black nylon
» Spray lacquer or poly- strings, Elderly #HCU. For $5, and #6 countersinking bit
urethane, clear (1 can) Aquila’s Nylgut set, Elderly » Screwdriver, Phillips head
» Sheet metal screw, 2", #ANCR, has the sound of old- » Spring clamps (2 or more)
pan head fashioned gut strings. » Hacksaw with fine-tooth blade
» Rotary tool with cut-off wheel
From a resale shop or From a grocery store:
department store: » Square wooden toothpicks (20) such as a Dremel
» Cake pans, aluminum or steel, » Needle files including a trian-
You can also get these from Lego
2" deep: 9" diameter (1) and Education (legoeducation.us), gular file
8" diameter (1) Cake pans item #W751742. » Rasp or Surform plane/rasp
have sides at right angles to the » Flush nippers, end cutters, toe-
bottom, and are deeper than
pie pans. Steel is OK, but rigid nail clippers, or a utility knife
aluminum pans are easier to cut
and have a better sound.

makezine.com 79

PROJECTS PANJOLELE

1. PREPARE THE 1a
NECK AND BRACE

1a. Using a power or hand
miter saw, cut 2 lengths from
the 1×2 board: 13¾" for the
neck and 10½" for the brace.
Save the leftover piece for
other parts.

1b. Decide which side will be 33" 2"
the fretted (top) side of the 45¡ 3¼"
neck, and use a sanding block
to sand it flat and smooth.
Start with coarser grits and
work up to finer grits.

1c. At one end of the topside 1c
of the neck, mark out the
cutout as shown. This is the
Panjolele's headstock.

1d. Carefully cut away the 1d 1d
wood from this area using
a handsaw and then sand 1¼" 2"
away any saw marks. 2¾"

1e. Mark out the placement
of the tuner holes as shown.
Drill the holes all the way
through the headstock using
a 6" drill bit.

1f. Following the same holes, 2"
drill down 1" from the top
of the headstock with a 2" 2" ½"
bit. Test the fit with one of
the tuners. TIPMark the bit

1e with a piece of tape
to help you stop at
1f the right depth.
80
NOTE These

hole dimensions fit
the UP26 tuners.
Adjust if necessary
to fit your tuner’s
shaft and bushing.

2.ATTACH THE NECK 2a
TO THE BRACE
TIPAlternately,
2a. Mark out the areas where
the neck and brace will join. use a bit slightly
Draw a line on the bottom of larger than the
the neck 1½" from the uncut unthreaded part of
end. Make a similar mark 1½" the screw’s shaft,
from one end of the brace.This then use a larger bit
is now the top of the brace. to countersink the
top of the hole.
2b. On the bottom of the 2" 2"
brace at this same end, mark 2" ¾" 2b
out the 3 holes as shown.
1¼"
Drill the holes all the way
through with a #6 screw
countersinking bit.

2c. Leaving one hole un- 2b 2d
covered, clamp the neck 2c
and the brace together on a
workbench with the 2 marked 6" 6"
areas facing each other and 2"
each edge squared up to the
marked lines.

Using the hole as a guide,
use the #6 bit to drill ½" into
the neck on the centerline,
fret side down, being careful
not to drill all the way through.

Install a #6 wood screw into
this hole and tighten well.

2" 2" 2"

2d. Remove the clamp, 9" 9"
recheck the alignment of the
2 pieces, and drill the other 2
holes. Install the remaining
wood screws to check for fit,
then remove all the screws.

2e. At the other end of the 2e
brace, mark out the string
holes as shown in the diagram.
Using a 5" bit, drill the holes
all the way through the brace.

2f. Measure 5" from this 2f
same end, and drill a 1" hole
through the brace, centered
from side to side.

makezine.com 81

PROJECTS PANJOLELE

3.LAY OUT AND 3a
GLUE THE FRETS
NOTE
3a. Using a pencil, mark a line
on the topside of the neck Double-check your
34" from the headstock end. measurements and
This is where you’ll glue be sure the lines are
the nut. square to one edge.

3b. Starting from this line, TIPTo keep
mark out the placement of
each fret as shown in the your fingers away
chart (below). from freshly glued
frets and do the job
3c. With a very small amount 3b faster, stagger the
of wood glue, glue one tooth- 3c gluing order: #1, #7,
pick at the headstock side of #2, #8, #3, #9, etc.
each line, and clamp carefully 3c
with a pair of spring clamps. 3c
Allow the glue to set for a
couple of minutes, remove
the clamps, and carefully wipe
away any excess glue with a
damp rag.

Set aside to completely
dry overnight.

Fret Placement Chart

Scale length: 15½"

Fret # Inches from nut
(to nearest e)

14

2 10

3 2p

4 36

5 34

6 4a

7 5t

8 5¾

9 6u

10 6q

11 7u

12 7¾

13 86

14 8s

15 9

16 9i

82

4.PREPARE THE How to Find the
CAKE PANS Center of a Circle

4a. On the back of the 9" Draw a line across the circle,
cake pan, mark the center near the edge. Measure that
and drill a 6" hole. line and divide it in half,
then use your adjustable
4b. On the back of the 8" 4b square to draw a second line
cake pan, mark the center from the midpoint, perpen-
and draw a line through it, dicular to the first.
from edge to edge. Draw
parallel lines ¾" on either Do this 2 more times.
side of this centerline. The 3 perpendicular lines
will intersect in the center
Transfer these parallel of the circle.
lines down each side.
4b
Between these lines, mark
a base line on each side ½" 4c
from the back of the pan,
using the adjustable square. 4d

4c. Using a hacksaw, cut a 4b TIPIf you use a
notch in the side of the pan
along the parallel lines, from saw like I did, clamp
the rolled top edge to your the toothpicks and cut
base line. downward to avoid
pulling off the frets.
Cut along the base line
with the rotary tool’s cutoff makezine.com 83
wheel. (You might also be
able to score, bend, and
snap the piece off.)

Repeat on the other end
of the pan.

4d. File away any burrs 4c
and test-fit the brace into 4d
the notches. If necessary, file
enough metal away for the
brace to fit.

5.SAND
THE FRETS

5a. Using a saw, pair of
flush nippers, end cutters,
toenail clippers, or utility
knife, carefully trim the ends
off of the toothpicks.

5a

PROJECTS PANJOLELE

5b. With medium-grit sand- 5b 5c
paper and a sanding block,
sand the edges of the tooth- CAUTION
picks flush with the edges
of the neck. You can also Don’t sand too much,
sand the ends of the frets as this will change
at a 45° angle. the maximum height
of the fret.
5c. With fine sandpaper and
a block, sand the tops of the
frets so that they’re all level.

5d. Sand the top edges of
each fret to make them nice
and round.

6.FINISH THE NECK 5d
AND BRACE
NOTE Stay
6a. Using a rasp or Surform
tool, ease over the corners of about 1/2" away from
the neck, and round the back. the headstock area and
the area that will be
6b. From the leftover parts of screwed to the brace.
the 1×2 (or other hardwood
scrap), cut the nut and bridge 6a 13" ½"
pieces as shown. File the Bridge ¼" 2" 2" 2" ¼"
notches with a triangular file.
6b 6" 2¼"
Glue the nut on the nut line Nut
on the fretboard side of the 6b 1½" 6"
neck, the same way you glued 1" 6b 9"
the frets. 1"
6b 2"
Set the bridge aside; you’ll
use it in the final assembly. 2"

6c. Sand the entire neck 2" 9"
smooth, removing all pencil 6"
lines and tool marks. Sand
the brace.

6d. Attach the neck and brace
with the 3 wood screws.

6e. Finish the entire neck/
brace assembly and the
bridge with spray lacquer
or polyurethane and allow
to dry completely.

6d 6e

84

7. FINAL
ASSEMBLY

7a. Press-fit the bushings into
the front of the headstock and
install the tuners.

7b. Put the 8" cake pan over 7a 7a
the brace, taking care not to 2nd string (tune to E) 1st string (tune to A)
scrape the wood finish.

7c. Tie a knot in the end of
each ukulele string and thread
them through the holes in the
end of the brace. Check the
diagram to get the placement
just right.

Thread the strings through
the holes in the tuners and
knot them. Turn the tuners
to tighten the strings.

7d. Attach the 9" cake pan
to the back of the brace with
the 2" pan head screw.

7e. Put the bridge under 7b
the strings and move it 153"
away from the nut. (The extra
1" compensates for any
string stretch.)

TEST BUILDER:
Josie Rushton,
MAKE Labs

7c 3rd string (tune to C) 4th string (tune to G)

When he’s not diligently avoiding work, Chester 7d 7e
Winowiecki makes functional pottery and musi- makezine.com 85
cal instruments from clay and other fun junk. He
lives a happy rural life with his artist wife, Cara
O’Brien, and their cat, Gizmo, in Whitehall, Mich.

PROJECTS PANJOLELE

Tuning up: Tune up your ukulele FINAL
with an electronic or online tuner, ADJUSTMENTS,
tuning the strings G-C-E-A (most TUNING & PLAYING
popular) or A-D-F#-B. Ukulele
strings take a long time to stop Resonation
stretching, so you’ll need to keep Nation
retuning for a couple days, but it’s
good practice! If the tuners turn Cara O’Brien
back after you let them go, tighten
the screw at the end of the tuner.

Fine-tuning the action: If the
strings feel really hard to push
down to the frets, you can lower
the “action” at the nut and the
bridge. The bottom of the strings
should be about ⅓2" from the top
of the first fret and 3⁄32" from the
top of the twelfth fret. Deepen the
notches in the nut first and then
sand the bottom of the bridge. Do a
little at a time, and check frequent-
ly so you don’t overdo it. If you find
that the strings pop out of the nut
or bridge, use a precision knife to
cut deeper slots.

Playing tunes: Here are few
chords to get you started. For right-
handers: use the fingers of your
left hand to press the strings down
to the frets in the spots shown in
the diagrams. The numbers under
each string show which finger to
use. Strum all 4 strings with the
first finger or thumb of your right
hand. Lefties: reverse!

Going further: Use this same
method to make instruments
with longer scale lengths, more or
fewer strings, metal frets and steel
strings, or different sound boxes.
One of my favorite instruments
right now is a tenor banjo with
4 steel strings, metal frets, a 21"
scale, and a cake-pan soundboard
and resonator.

86

Dice Popper

By Gus Dassios Illustrations by Julie West

THIS IS MY VERSION OF A CLASSIC WAY YOU WILL NEED: Plastic capsule, 2"
to “roll” the die for a board game. The key to
making this special die agitator is the clear diameter » Die » Compression spring, ⅜"
plastic capsule. I found the right size, 2" diam- diameter, 2"-long, .035" wire diameter »
eter and 14" tall, in a vending machine — it’s Wood, ¼"-thick and ¾"-thick » Flathead wood
the kind that holds inexpensive toys or trinkets. screws, #8×¾" (4) » Finishing nails, 1¾"-
long, small (4) » Electric drill and drill bits »
1. Cut the wood. Hole saw » Saw » Hammer » Screwdriver

Parts A, C, and E are cut of ¼"-thick wood,
while parts B and D are ¾" thick. Cut all
5 pieces to 3½"×3½".

2. Drill the holes.

»Holes have to be drilled in all pieces except

part E. For part A, cut a large hole in the
center, anywhere from 1⅞" to 2" in diameter,
depending on the size of the domed half of
your capsule. Then drill 4 countersink holes

»about ½" in from each corner, for the wood

screws. For parts B and C, cut a 2⅛"-
diameter hole in each center. These holes
will house the bottom part of the capsule.
For part D, drill a ⅜"-diameter hole in the
center, which provides a guide for the spring.

3. Assemble.

Nail together parts B through E with the
finishing nails, avoiding the corners where
the screws will go. After this bottom block
is assembled, insert the spring. Place a die
into the capsule, snap it, and lower it into
the wood block. Part A will cap everything.
It requires a slight push to keep it in place

»as you screw in the wood screws. After

that, you’re ready to go. Good luck! a

Gus Dassios lives, designs, and builds in Toronto, Ontario.

makezine.com 87

PROJECTS GHOST CHILIES

The Bhut Jolokia
pepper is 125 times
hotter than a jalapeño.

Written and photographed by
Gabriel Nagmay
Illustrated by Evan Hughes

a TIME: SEVERAL MONTHS a COMPLEXITY: EASY

Right now, under some lights in my basement, sit several dozen
pots of soil. Out of each sprouts a small seedling, only a few
millimeters high — a humble beginning for plants that will grow
to produce one of the hottest peppers on the face of the Earth:
the Bhut Jolokia, commonly known as the ghost chili.

THE BHUT JOLOKIA FIRST CAME TO MY and setup ready by mid-February.
ATTENTION IN 2007, when Guinness World My indoor setup is simple. On a table in the
Records crowned it “world’s hottest chili
pepper” (though it’s since been deposed by basement, I have a seed starting tray, a heat-
another). Certified at well over 1,000,000 ing pad, and lights. The tray is divided into 72
Scoville heat units, the fruit from this plant is cells, each holding a few cubic inches of soil.
125 times hotter than the spiciest jalapeño.
Fill the cells with soil and place a single seed
At the time, tracking down seed stock on top of each. No need to cover them; all they
for the pepper was a challenge. I was lucky require for germination are the proper mois-
enough to have a friend of a friend who worked ture and temperature. Thoroughly water the
for New Mexico State University’s Chile Pepper seeds and set the tray on the heating pad.
Institute (chilepepperinstitute.org).
Keep the soil moist and warm, between
These days, seeds can be purchased from 75°F–90°F. You can use a digital oven ther-
online retailers or from private growers on mometer to track the temperature. With luck,
Amazon and eBay. There are even “just add roots should emerge from each seed in 7–14
water” kits. Skip these. Chili peppers are easy days. (Bhut Jolokia seeds will germinate at
to grow — once you know a few tips. temperatures as cool as 65°F, but it’ll take
30+ days, and many seeds may fail.)
MATERIALS & TOOLS
Once they emerge, your tiny plants will
» Bhut Jolokia chili pepper seeds available online require a good source of light. Since you’re
» Seed starting tray with soil doing this in the winter, indoor lighting is your
» Pots, 3" or 4" (one per seedling) best option. Fluorescent tubes are inexpensive
» Fertilizer, nitrogen rich, such as 10-5-5 and efficient, and they work well. Hang them
above the plants with wire so you can adjust
or composted manure the height. It’s important to keep them only a
» Fertilizer, 5-10-10 few inches above the top of the peppers; any
» Heating pad higher, and the plants will grow spindly. Leave
» Grow lights the lights on 24 hours a day to give your pep-
» Digital oven thermometer pers a jump-start on the season.

The first set of leaves will be tiny and round.
As each seedling establishes its root system,
a second set of leaves will appear. When these
“true leaves” emerge, transplant the peppers
into 3"–4" pots. Over the next couple months,
your plants will have room to grow a healthy
root system and several more sets of dark
green leaves.

1. Start your seeds. 2. Move the plants outdoors.

Chili peppers require a long growing season Peppers require full sun and well-drained soil.
to produce mature fruit. In northern climates, I’ve found that raised beds or 2gal pots both
it’s best to start your seeds indoors up to 3 work well. After the last chance of frost, you
months before the last frost date, allowing the can move your plants outside. Just be careful
plants plenty of time to germinate and grow a — a single cold night (below 50°F) will deci-
few sets of leaves before they’re transplanted mate your chilies.
outside. For me, this means getting my seeds
The most important tip to remember when
gardening: try to mimic the environment
where your plants would thrive naturally.
These peppers are from the Assam region of
India, where summer temperatures can reach

makezine.com 89

PROJECTS GHOST CHILIES

When transplanting your ghost
chilies outside, keep them cozy
with mini greenhouses made of
2-liter soda bottles.

Use a nitrogen-rich fertilizer
for the first month to promote
rapid foliage growth, giving
your peppers their best chance
of producing a bumper crop of
extreme hotness.

100°F. They also do well with high humidity. If you live in Ghost Sauce
a northern part of the United States (like me), you might
have to improvise. This delicious Belizean-style hot
sauce will highlight your home-
If you don’t have row covers to keep the temperature grown Bhut Jolokia chilies. Adjust
up, you can make a mini greenhouse for each plant. the peppers to taste: 2.5oz gives
Cut the bottom off a clear, 2-liter soda bottle and place good heat without overpowering
it over each start. This has the added benefit of keeping the flavor. Any more, and you
out slugs, cutworms, and other pests. Just keep an eye may want a warning label.
on the temperature inside the bottle; too much heat
will turn the mini greenhouse into a solar oven. The cap 1. Sauté ½c white onion.
can be removed to provide ventilation.
2. Add 1c water, 2tbsp fresh lime
During the first few weeks outdoors, a nitrogen-rich
fertilizer will help the plant grow tall and strong. At the juice, 2tbsp white vinegar, ½tsp
time of planting, apply either composted manure or salt, 1 chopped garlic clove, and
a slow-release fertilizer such as 10-5-5. These numbers ½c shredded carrot. Bring to a
correspond to the nitrogen (N), phosphorus (P), and simmer, then turn off the stove.
potassium (K) available in the fertilizer. The higher levels
of nitrogen will promote rapid foliage growth, giving 3. Add 2.5oz chilies, chopped.
the plant a chance to thrive. You may soon need to add
a stake or cage to support the plant. Wear gloves when handling them.

90 4. Blend and enjoy!

Each pepper is so potent that
even minimal contact can
numb your fingertips.

Regular watering and proper fertilization 3. Harvest your peppers.
throughout the hot summer months will
ensure that your pepper plants continue Pick individual peppers as they ripen. A fully
to thrive. However, after the first month in ripe Bhut Jolokia pod is completely red and
the ground, consider switching to a 5-10-10 has a glossy, wrinkled texture.
fertilizer. This mixture contains half as much
nitrogen as phosphate and potassium. High At this point, your peppers have developed
nitrogen promotes foliage growth, but it may the maximum amount of capsaicin, so be
do so at the cost of flower and fruit produc- careful when handling them. Most of this heat
tion. You could easily end up with a huge green chemical is contained on the ridges inside
plant that never produces a single pepper. the fruit where the seeds are held. However,
it’s a good idea to wear gloves when handling
As summer comes to an end, you should the fruit. Each pepper is so potent that even
have a mature Bhut Jolokia plant covered in minimal contact can numb your fingertips.
2"–3"-long, distinctly wrinkled, green peppers.
Your goal is to let the peppers ripen on the Another advantage of picking the peppers
vine, giving them time to produce the most fully ripe is seed saving. Each mature fruit
capsaicin — the chemical compound that contains about a dozen seeds. Carefully
makes peppers taste hot — but two things collect these. They’ll stay viable for several
can easily ruin your crop: frost and birds. years if stored in a cool, dry place.

Any temperature below 50°F may cause 4. Use your ghost chilies.
the plant to drop fruit prematurely. On cool
nights, cover your peppers with a row cover or Armed with an arsenal of fully ripe ghost
a thin sheet to trap warm air around the plant. chilies, you now have many usage options to
If extended cold weather is in the forecast, choose from. You can hang them around your
you might even dig it up and bring it indoors. home to protect from wild elephant attacks.
You can extract the capsaicin to produce a
The other enemy: birds. In India, people potent, homemade pepper spray. Or, like me,
use these blazing-hot peppers to ward off you can use them as the key ingredient in my
elephants, but unfortunately birds seem to be kick-ass Ghost Sauce recipe. Enjoy!
immune to capsaicin. Crows, ravens, and oth-
ers will be attracted to the bright red fruit and Gabriel Nagmay (gabriel.nagmay.com) is a web geek living in Portland, Ore.,
will happily steal it as it begins to ripen. Try who loves building tall bikes, brewing beer, and growing unusual edibles.
bird netting or other measures to deter them.

makezine.com 91

PROJECTS ELECTRONICS: FUN & FUNDAMENTALS MATERIALS

Key-Card » Phototransistors, visible spec-
Door Lock trum (6) Everlight part #PT334-
6C or RadioShack #55053303
Pick-proof, programmable security
without a microcontroller. » LEDs, white, water-clear (3)
typical 3.3V forward voltage,
Written and illustrated by Charles Platt minimum, 5,000mcd with
30° dispersion; Kingbright
a TIME: 2 HOURS—2 DAYS #WP7104VW1C or RadioShack
a COMPLEXITY: MODERATE TO HIGH #55050632

Almost anyone can learn to pick a typical door lock. » Slide switches, subminiature
The most common method is to jiggle the tumblers DPDT (6) C&K #OS202013
by inserting a tool known as a “rake,” while apply- MT5QN1
ing turning force with a tension wrench. When the
tumblers are aligned, the cylinder rotates and you » Toggle switch, DPDT, center-
can walk right in. off momentary, minimum 3A
Mountain Switch #108-0005-EVX
When I first started thinking about a pick-proof elec-
tronic lock, I imagined a totally automated system using » Resistor arrays, bussed,
a key card and a motor that would pull a deadbolt aside. 5.6K (2) Xicon #265-5.6K-RC
However, a motor that was powerful enough to overcome
the likely friction would require either 115V AC (vulnerable » Logic chip, triple 3-input
to power outages) or a substantial battery. AND gates, type 74HC11 Texas
Instruments #SN74HC11N
It would be cheaper and simpler to use an off-the-shelf
deadbolt that’s moved manually by turning an external » Darlington transistor, 8A, type
knob. I could block or unblock the movement of the dead- 2N6043 On Semiconductor
bolt using a small, low-power DC gearmotor to turn a lever, #2N6043G
as shown in Figure A.
» Mini lever snap switches,
For the key card, I imagined a plastic rectangle punched SPDT, 5A (4) maximum 20g
with a unique pattern of holes. The card would slide into operating force, Mountain Switch
a slot with a light source to shine through the holes to pho- #101-1206-EV
totransistors beneath. Additional electronics would decide
whether the pattern was correct. If I needed to rekey the » Diodes, general purpose, 3A
lock, I could make a new card with a different pattern, and (2) Vishay #SRP300G-E3/54
reprogram the electronics to match.
» Voltage regulator, 5V, type
The word “reprogram” suggested I’d need a microcon- LM7805 Fairchild Semiconductor
troller to complete this project. Or would I? Maybe a set of #LM7805CT or RadioShack
switches could do the job more simply and cheaply. The #276-1770
first step toward figuring this out was to review the way in
which phototransistors generally behave. » Capacitors, multilayer ceramic:
1μF (1), 0.1μF (1) for smoothing
92 the 5V output

» Gearmotor, 9V or 12V DC,
minimum 10rpm ServoCity
#RZ12-300-10RPM or check
eBay for substitutes

» 9V battery

Optional, recommended
for testing:
» Breadboard
» Jumper wires

For the finished project:
» Keyless deadbolt
» Opaque plastic to make key

cards and mounting panel
for switches
» Plywood, plastic, or aluminum
sheet to fabricate card slot

TOOLS

» Multimeter and test leads
» Soldering iron and solder
» Wire cutters and strippers

Fig. A: In this simplified rendering, a deadbolt (blue)
is turned by an external knob (gray). The sliding shaft
(red) is either blocked or freed by a lever (yellow)
driven by a motor (purple) mounted inside the door.
Limit switches (green) stop the motor when the
lever reaches either end of its travel. A third switch
beneath the sliding shaft shuts down power when
the deadbolt retracts, to prevent the motor from
fouling it and burning out. A fixed block (gray) resists
the force transmitted through the lever if someone
tries to jimmy the closed lock.

Phototransistors Basics pattern is correct. This can be verified by
ANDing all the phototransistor states via a
In Figure B (following page), the photo- logic chip, because an AND gate only outputs
transistor is the circle with arrows suggesting high if all its inputs are high.
incoming light. When the light is off, the photo-
transistor allows only a tiny leakage current A hardwired array of phototransistors is
between emitter and collector, and the voltage not reprogrammable, but I saw that a DPDT
between point X and ground is almost zero. switch could solve the problem, as shown
As the light increases, the phototransistor in Figure D. In its “up” position the switch
junction becomes saturated, just like an NPN emulates the circuit in Figure B. In its “down”
transistor when the base is highly biased. position the switch emulates the circuit in
The effective internal resistance drops, and Figure C. If the key card pattern is changed,
the voltage at point X rises close to the supply the switch positions are changed to match.
voltage (assuming any electronics attached
to X have high impedance). I found a 5.6K Phototransistors and subminiature slide
resistor worked well with the phototransistor switches are cheap, so the electronics for this
I chose for this project. project shouldn’t cost more than $20. The
motor and deadbolt are extra, but I found
If the positions of the phototransistor and small DC motors on eBay for $5 or $6 each.
the resistor are reversed, the outcome is too.
In Figure C, when the phototransistor is dark Combinations
and blocks current, the voltage at X is high.
When light shines on the phototransistor, the Now to decide how many phototransistors to
voltage at X goes low. use. Sixteen in a 4×4 grid would allow 65,536
possible combinations, which sounded rea-
So, depending on wiring, a phototransistor sonably secure. But 16 phototransistors, 16
can give a high output either in the light switches, and 32 resistors is a lot to wire. Then
(Figure B) or in the dark (Figure C). Thus, if I realized most of the holes in the card could
phototransistors are wired as in Figure B to be dummies. Six phototransistors would still
match the holes in a key card, and as in Figure provide 64 possible combinations for the lock.
C to match the blocked areas of the card, all I would be the only person who knew which
their outputs will go high when the card’s holes were dummies, and which were not.

makezine.com 93

PROJECTS ELECTRONICS: FUN & FUNDAMENTALS

5V DC 5V DC 5V DC

5.6K 5.6K
X
X
5.6K X

BC 5.6K

Fig. B: Voltage at point X is high when light falls on the D
phototransistor, and low when the phototransistor is dark.
Fig. C: Voltage at point X is low when light falls on the until a key card is inserted. This switch should
phototransistor, and high when the phototransistor is dark. be positioned so the card closes it when slid
Fig. D: A DPDT switch enables a single circuit to emulate fully in.
both of the configurations in Figure B and Figure C.
Because the motor will burn out if it tries to
Next, how to AND 6 phototransistor out- turn the lever to block the deadbolt when the
puts? This is easy using a 74HC11 chip with deadbolt has already been retracted, I needed
three 3-input AND gates. Figure E shows how one more fail-safe switch. This is S8, which
they’re chained to give a single output. shuts off the power when the opening dead-
bolt rubs against it.
These phototransistors can be connected
directly to the chip because they comply with More Details
its requirement for a high input no less than
3.5V and a low input no greater than 1V DC. If you use a really small gearmotor rated for
Use a meter to verify your phototransistors 9 or 12V DC, the whole lock can be powered
also meet this requirement. by a 9V battery. An LM7805 voltage regulator
(not shown) will reduce its output to the 5V
Additional Switches required by the phototransistors and the chip.
The LM7805 datasheet, online, will show you
The chip’s output controls a Darlington tran- how it should be used in conjunction with a
sistor, which powers the motor (Figure F). The couple of bypass capacitors.
motor stops itself at each end of its travel by
opening one of a pair of limit switches, marked Because the motor is reversed by chang-
S5 and S6. (If you’re unclear about how limit ing the polarity of the power, I couldn’t add a
switches work, you’ll find a detailed explana- protection diode to divert the surge that the
tion in my book Make: Electronics.) motor takes when it starts or stops. If you find
that the power spike disturbs your logic chip,
S4 is a manual DPDT switch, spring-loaded try putting a 0.1 microfarad (μF) capacitor
to return to its center-off position. It starts the between the positive power supply to the chip,
motor in one direction or the other by bypass- on pin 14, and the negative supply on pin 7.
ing either S5 or S6 through a rectifier diode.
If your motor doesn’t respond appropriately, The resistors in series with the phototrans-
just swap the wires to its inputs. istors are all 5.6K. To simplify wiring and save
space, I used a pair of resistor arrays. Check
The purpose of S7 is to minimize battery the datasheet online for the resistor array to
drain by keeping the circuit powered down

94

Output Inputs from 3 Fig. E: The internal arrangement of three
phototransistors 3-input AND gates in a 74HC11 chip, and how
they can be chained to AND 6 inputs.
1 14
2 13 Fig. F: The complete schematic. Three of the
3 12 phototransistors have been omitted to save
4 11 space, but are wired just like the other three.
5 10
69 Fig. G: Breadboard proof-of-concept. Six
78 phototransitors wired “light-high” are correctly
ANDed, illuminating the LED.
“Always On” Inputs from 3
unused input phototransistors see how the resistors are wired inside.
You may want to add an LED indi-
E S2 S3
cator outside the lock, tied to the
5V DC output from the Darlington transis-
tor, to let you know that the key has
S1 been accepted and the position of the
deadbolt can now be changed.
220
S8 Last but not least, you’ll need a
light source to activate the phototran-
Gunther Kirsch (G) S4 74HC11 sistors. Many phototransistors are
S5 S6 only sensitive to infrared, but the type
S7 From other 3 I chose will respond to a very broad
Motor phototransistor spectrum, so you should be able
to use 3 bright white LEDs to shine
9V DC circuits down upon the key card. Wire them in
series, and you can power them with
F 9V DC and no additional load resistor.

G As for interfacing the motor with
the deadbolt, this mechanical issue is
outside the scope of this column, but
the setup should look basically like
Figure A. I leave it to you to determine
the details of fabricating a card slot
and mounting it in the door.

Can this lock be broken? Of course!
If someone uses enough brute force,
almost any door will yield. Still, the
electronic lock will be considerably
more secure than a traditional lock
containing mechanical tumblers.

Get Charles’ books, Make:
Electronics and the Encyclopedia of
Electronic Components Vol. 1 from
the Maker Shed: makershed.com.

An author and a contributing editor of MAKE, Charles Platt
designs and builds medical equipment prototypes in Arizona.

makezine.com 95

PROJECTS OPTICAL TREMOLO

Optical Plug your
guitar into light-
programmable
waveforms with
this unique
effects box.

Written and photographed
by Sean Michael Ragan

Tremolo Box
a TIME: 5 HOURS a COMPLEXITY: MODERATE

MAKE contributing editor Charles Platt proposed a ”Hypothetical Tremolo
Wheel” in his article about online DIY guitar stomp-box communities (MAKE
Volume 15, page 82, ”Stomp Box Basics: Tremolo and Fuzz”). Well, it’s hypo-
thetical no more. I took Platt’s cue and built this Optical Tremolo Box, which
reads a patterned disk with a light sensor to create a warbling volume effect
(tremolo) that you can custom-program with any pattern you like.

To 100K To
Guitar Amp

Photoresistor

251 151 +3V

DPDT toggle
(center-off)

How It Works

OFF OFF OFF

Gregory Hayes; Rob Nance (illustration) How does tremolo work? What if you bridge the And here’s where Platt
So there’s your electric gui- 2 wires with a resistor had a clever idea: use a
tar, the amplifier it’s plugged instead? With a strong resistor that responds to
into, and the cable that runs resistor, nothing happens — light. Wave your hand in
between them. Open up that it’s still easier for the charge front of the photoresistor,
cable and you’ll find 2 wires to go through the amp. and the volume will respond
— one “ground” and one held With a really weak resistor, to the shadow of your hand.
at a positive voltage relative the sound cuts out. With a Mount a spinning disk with
to “ground.” The changing resistor in the middle range, alternating clear and opaque
electrical potential between the sound will be quieted, bands in front of it, and the
the wires, over time, is what but not completely muted, volume will follow the pat-
carries the sound signal. as the charge divides itself tern on the disk, repeating
between short and signal as it spins. That’s tremolo — a
What happens if you pathways. Use a variable repeating variation in volume
short-circuit those wires, resistor, and you have a over time.
bridging them with a third crude volume control: turn
wire? The sound goes away. the resistance way up, the Intrigued? Want to try
The charge can find its way sound will be loud; turn it building one? I thought you
home now, via the short, way down, and the sound might. Let’s get started.
without ever bothering to will vanish.
go all the way through your
amplifier. And so it does.

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PROJECTS OPTICAL TREMOLO

MATERIALS TOOLS

» Adhesive label, 8.5"×11", » Grommet, rubber, 2" ID » Computer and printer
printable × 3" OD × ½" mounting hole » Drill and 1" drill bit
diameter » File
» Project enclosure, plastic, » Hacksaw
6"×3"×2" » Transparency film, printable, » Lighter
8.5"×11" » Multimeter
» Rheostat, 25Ω » Pliers, needlenose
» Resistor, 15Ω » Terminal strip, 8-position, » Scissors
» Control knobs, for ¼" shafts (2) European-style » Screwdrivers: Phillips
» Hookup wire
» Potentiometer, 10kΩ » Universal mounting hub for and r" flat-blade
» CdS photoresistors (5-pack), 3mm shafts, Pololu #1079 » Soldering iron and solder
» Unibit aka step bit
RadioShack #276-1657 » Battery holder, 2×AA, enclosed, » Wire cutter/stripper
» LED holder with leads » Wrenches, box end: 10mm,
» Switch, DPDT, with center
» DC power plug, coaxial, size M 11mm, 12mm, 14mm
off position » Heat-shrink tubing multicolor » X-Acto knife
» Adhesive tape, double-
assortment
sided, foam » Hook-and-loop fasteners,
» Jack, DC power, size M
» Jacks, ¼", TS/mono (2) adhesive, coin shape, 3"
» Motor, 1.5–3 V DC aka velcro dots
» Plastic tubing, 2" long × 2mm » Power supply, wall adapter,
3V DC, with size M plug
ID × 3mm OD I used the ink tube » AA batteries (2)
from a Bic Soft Feel retractable » Cushion feet, jumbo,
ballpoint pen, medium point. self-stick (3)
» Wood screws, #4 size, » Micro flex light Coast model
¼" length (2) 7578 series

B

A 1.DRILL THE ENCLOSURE 2.MOUNT THE
RHEOSTAT
TIPA bit of Download the drilling template from
makeprojects.com/v/33 and print it onto This knob controls the motor
rubbing alcohol a full-page adhesive-backed mailing label. speed. First, bend all 3 con-
can help if the tacts on the rheostat down
templates don’t Cut out the 4 template sections, peel off 90°, parallel to the shaft. Then
come away cleanly. the backing, and affix them to the front, top, turn the rheostat all the way
and sides of the enclosure box. “down” (counterclockwise).

Drill the holes where marked. Start each We add a 15Ω resistor,
hole with a 1" brad-point bit, then switch in series, to bias the range
to a unibit to drill the bigger holes (Figure A). toward the slower speeds,
which are more useful for
Peel off the templates and discard. tremolo effects. Solder one
lead of the resistor to the
rheostat center contact and
the other to a 3" length of
wire (Figure B).

Use your multimeter to
check the resistance between
the center wire and each of
the other 2 rheostat con-
tacts. One of them should
read about 15Ω and the other
about 40Ω. Solder a 4" length
of wire to the 40Ω contact.
Cover the resistor and all

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